5B Nutrient Cycles

Question 1

What role do bacteria play in nutrient recycling

Answer 1

Many are saprobionts - they feed on the remains and waste products of dead animals and plant. This allows important chemical elements in the remains to be recycled
Saprobionts secrete enzymes, and digest their food externally and then absorb the nutrients they need - extracellular digestion. During this process organic molecules are broken down into inorganic ions - saprobiotic nutrition

Question 2

What are symbiotic relationships

Answer 2

known as mycorrhizae
fungi made up of long and thin strands called hypae which connect to the plants roots these increase the surface area of the plants roots helping them to absorb ions from the soil and increase the uptake of water

In turn, the fungi obtain organic compounds from the plant

Question 3

What is nitrogen used for in plants and animals

Answer 3

to make proteins and nucleic acids

Question 4

Describe stage 1 of the nitrogen cycle - nitrogen fixation

Answer 4

Nitrogen fixation - where nitrogen gas in converted into nitrogen containing compounds this is carried out by bacteria who turn nitrogen into ammonia ions in solution

Rhizobium are found inside root nodules of leguminous plants they form a mutualistic relationship with the plants - they provide the plant with nitrogen compounds and the plant provides them with carbohydrates

Question 5

Describe stage 2 of the nitrogen cycle - Ammonification

Answer 5

Ammonification - when nitrogen compounds from dead organisms and animal waste are turned into ammonia by saprobiotics which goes on to form ammonia ions

Question 6

Describe stage 3 of the nitrogen cycle - Nitrification

Answer 6

Nitrification - when ammonium ions in the soil are converted into nitrogen compounds that can be used by plants
First nitrifying bacteria called Nitrosomonas change ammonia ions into nitrites
Then other nitrifying bacteria called Nitrobacter convert nitrites into nitrates

Question 7

Describe stage 4 of the nitrogen cycle - Denitrification

Answer 7

Denitrification - when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria - use nitrates in the soil for respiration and produce nitrogen gas
This happen under anaerobic conditions eg in waterlogged soils

Question 8

Describe the phosphorus cycle

Answer 8

1. Phosphate ions in rocks are released into the soil by weathering
2. Phosphate ions are taken into the plant through the roots. Mycorrhizae greatly increase the rate in which phosphorus can be assimilated
3. Phosphate ions are transferred through the food chain as animals eats the plants and are then eaten by other animals
4. Phosphate ions are lost from animals in waste products
5. When plants and animals die, saprobiotics are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation by plants. These microorganisms also release the phosphate ions from urine and faeces
6. Weathering of rocks also releases phosphate ions into seas, lakes and rivers. This is taken up by aquatic producers, and passed along the food chain to birds
7. The waste produces by birds are known as guano and contains a high proportion of phosphate ions. Guano returns a significant amount of phosphate ions to soils which is often used as natural fertiliser